1. Field of the Invention
The present invention relates to a sewing machine shuttle that works together with a needle and take-up lever to form stitches on fabric.
2. Description of Related Art
Japanese laid-open patent publication number Hei 6-327873 (xe2x80x9cJP ""873xe2x80x9d) describes a sewing machine shuttle as shown in FIGS. 10A-10C. This sewing machine shuttle 50 is equipped with an outer shuttle 52 rotated by a shuttle drive shaft 51 and an inner shuttle 53 housed inside the outer shuttle 52 so that rotation relative to the outer shuttle 52 is possible. A needle guide hole 54 is formed on the upper surface of the inner shuttle 53 and a rotation stopping recess portion 55 is formed on the front surface of the inner shuttle 53 in phase alignment with the hole 54. A rotation stopping projection 57 of a shuttle stopping member 56 is loosely fitted in the rotation stopping recess portion 55. The rotation stopping projection 57 stops the rotation of the inner shuttle 53. An upper thread grasping section 58 and a guide plate 59 (referred to as a xe2x80x9cspringxe2x80x9d) are disposed on the outer perimeter of the outer shuttle 52. On the rear side, in terms of the rotation direction of the outer shuttle, is formed an upper thread advancing projection 61 for feeding the upper thread forward. The projection 61 projects forward to the front edge of the guide plate 59.
When a needle 62 rises slightly from the bottom dead center, the upper thread grasping section 58 grasps an upper thread Ta behind the needle 62. As the outer shuttle 52 rotates, an upper thread loop is formed around the inner shuttle 53. As FIG. 10A shows, as the upper thread loop expands, the upper thread advancing projection 61 pushes the upper thread Ta forward above the inner shuttle 53 so that the upper thread loop is pushed out from the outer perimeter surface of the inner shuttle 53 toward the front. As FIG. 10B shows, when the upper thread grasping section 58 reaches the lowermost section of the inner shuttle 53, the upper thread Ta enters a gap between the rotation stopping recess portion 55 and the rotation stopping projection 57. As FIG. 10C shows, the upper thread loop slides through the inner shuttle 53. When the upper thread grasping section 58 is oriented upward, a take-up lever (not shown in the figure) pulls up the upper thread Ta. This upward pulling force from the take-up lever causes the upper thread Ta to slip through the abutment of the rotation stopping recess portion 55 and the rotation stopping projection 57 toward the rear, in terms of the rotation direction of the outer shuttle, and the upper thread Ta disengages from the inner shuttle 53. Then, the upper thread Ta engages with a lower thread Tb, forming a stitch in the fabric W.
Japanese laid-open patent publication number Hei 11-244566 (xe2x80x9cJP ""566xe2x80x9d) describes a sewing machine shuttle shown in FIGS. 11A and 11B. This sewing machine shuttle 70 is equipped with an abutment section 74 disposed on the outer perimeter of an inner shuttle 71. On a shuttle-stopping member 75, there is disposed a rotation stopping projection 76 loosely fitted in a rotation stopping recess portion 72 and a stopper 77 engaging with an abutment section 74. When an outer shuttle 73 rotates, the abutment section 74 comes in contact with the stopper 77. The shuttle-stopping member 75 is attached to a shuttle support body (not shown in the figure) in a manner that allows its position to be adjusted. By adjusting, ahead of time, the abutment position of the abutment section 74 and the stopper 77, the gap between the rotation stopping recess portion 72 and the rotation stopping projection 76 can be made uniform both forward and back (in the direction of the rotation of the outer shuttle). Then, as shown in FIG. 11B, when the take-up lever pulls up the upper thread Ta, the upper thread Ta passes from front to back (relative to the rotation of the outer shuttle) through the gap between the rotation stopping recess portion 72 and the rotation stopping projection 76, passing out of the inner shuttle 71. With the sewing machine shuttle 50 of JP ""873, however, an upward pulling force from the take-up lever is used on the upper thread Ta to disengage the upper thread Ta from the inner shuttle 53 by pulling it out from the abutment between the rotation stopping recess portion 55 and the rotation stopping projection 57. As a result, the upper thread Ta receives a large resistance, leading to uneven tightness in the thread or, at times, breakage due to excessive tension. With the sewing machine shuttle 70 of JP ""566, a gap that is uniform both forward and back is maintained for the rotation stopping projection 76, thus allowing resistance acting on the upper thread Ta to be kept low. However, since this gap changes according to the position of the shuttle-stopping member 75, it is necessary to make tedious fine adjustments to positioning each time the shuttle-stopping member 75 is disassembled for replacement and cleaning.
The object of the present invention is to overcome the problems described above and to provide a sewing machine shuttle that allows, prior to the application of an upward-pulling force from a take-up lever and without the use of this upward-pulling force, an upper thread to be pulled from an internal shuttle while sliding through the abutment between a rotation stopping recess portion and a rotation stopping projection; prevents thread breakage and inconsistency in thread tension by avoiding resistance from the upper thread when the upward-pulling force of the take-up lever is applied; and stabilizes the action of the upper thread after it has been pulled from the inner shuttle.
In order to achieve the object described above, the sewing machine shuttle according to the present invention includes an outer shuttle rotated by a shuttle driving shaft, an inner shuttle housed in the outer shuttle rotatably relative to the outer shuttle, an upper thread grasping section disposed on the outer shuttle, a rotation stopping recess portion formed on the front side of the inner shuttle, a shuttle stopping member having a rotation stopping projection, said a rotation stopping projection being fitted loosely into the rotation stopping recess portion to allow the rotation of the inner shuttle to be stopped, and a projecting-forward upper thread release projection disposed on the front surface of the outer shuttle. While the upper thread grasping section is grasping and pulling the upper thread, the upper thread release projection pushes forward the upper thread which is droppped into the rotation stopping recess portion. This allows the upper thread to be slide out from the inner shuttle by being slid through the abutment between the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion and rotation stopping projection.
In the sewing machine shuttle of the present invention, when the outer shuttle is rotated, the upper thread grasping section grasps the upper thread and an upper thread loop is formed around the inner shuttle. As the upper-thread loop is expanding, it drops into the rotation stopping recess portion of the front surface of the inner shuttle. Then, when the upper thread release projection reaches substantially same phase as the rotation stopping recess portion, the upper thread release projection pushes the upper thread forward as described above so that the upper thread slides through the abutment between the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion and rotation stopping projection. In order to have the upper thread slide through the abutment with no misalignment, it would be preferable for the upper thread to be positioned near the abutment, i.e., at the rear side, in terms of the rotation of the outer shuttle of the rotation stopping recess portion.
In order to have the upper thread positioned at the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion, it would be preferable for the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion to be formed at a phase of 0xc2x0 to 40xc2x0 ahead, and, more preferably, at a phase of 3xc2x0 to 30xc2x0 ahead, forward in terms of the direction of rotation of the outer shuttle, of the vertical motion path of the needle (see a in FIG. 1). If the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion is positioned at a phase more than 0xc2x0 behind, the position within the rotation stopping recess portion of the upper thread will not be fixed. Thus, when the upper thread release projection pushes the upper thread forward, the upper thread may get caught at, for example, the tip of the rotation stopping projection so that it cannot slide through the abutment. On the other hand, if the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion is positioned at a phase of more than 40xc2x0 ahead, forming the rotation stopping recess portion becomes more difficult.
It would also be preferable to dispose an upper thread guide surface at the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion, the upper thread guide surface being more concave further in. As a result, when the upper thread release projection pushes forward the upper thread dropped into the rotation stopping recess portion, the upper thread pushes out forward along the upper thread guide surface. This provides reliable guidance of the upper thread to the abutment between the rear side, in terms of the rotation of the outer shuttle, of the rotation stopping recess portion and the rotation stopping projection.
While the upper thread grasping section is grasping the upper thread, the upper thread release projection can use the tension on the upper thread to push the upper thread out from the rotation stopping recess portion smoothly. In order to use this upper-thread tension effectively, it would be preferable to position the upper thread release projection at a phase delay of 160xc2x0 to 190xc2x0 toward the rear side in terms of the direction of rotation of the outer shuttle relative to the upper thread grasping section (the position of this section changes with rotation). As a result, the upper thread is popped out toward the outer perimeter of the inner shuttle from the rotation stopping recess portion and is prevented from getting caught at the corner of the rotation stopping recess portion. After the upper thread has disengaged, the tension of the upper thread is reduced and an upper-thread loop shape can be formed in a stable manner before the upper thread is pulled up by the take-up lever.
The upper thread release projection of the present invention can also be implemented in combination with the upper thread advancing projection in JP ""873. More specifically, an upper thread advancing projection is disposed on the front surface of the outer shuttle at a position in front of the upper thread release projection. Before the upper thread release projection pushes the upper thread forward, the upper thread advancing projection pushes the upper thread forward so that the upper thread is pushed toward the front side of the inner shuttle. As a result, at the initial stage of loop formation in the upper thread, the upper thread Ta applied to the outer perimeter surface of the inner shuttle is pushed toward the front side of the inner shuttle by the upper thread advancing projection so that the upper thread drops into the rotation stopping recess portion quickly. Then, the upper thread release projection can push the upper thread reliably from the rotation stopping recess portion. In order to provide accurate timing of the operations of the upper thread advancing projection and the upper thread release projection, it would be preferable to have the upper thread advancing projection positioned relative to the upper thread release projection (whose position will change with rotation) at a phase of 70xc2x0-90xc2x0 ahead of the release projection, forward in terms of the direction of rotation of the outer shuttle.
Further objects of this invention will become evident upon an understanding of the illustrative embodiments described below. Various advantages not specifically referred to herein but within the scope of the instant invention will occur to one skilled in the art upon practice of the presently disclosed invention. The following examples and embodiments are illustrative and not seen to limit the scope of the invention.